The superstitious symbolism of a black cat crossing one's path is dependent upon culture: some cultures consider this a sign of impending bad luck, while some cultures consider this a sign of impending good luck.
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Opening an umbrella indoors is said to result in 21 days of bad luck. Some traditions hold that it is only bad luck if the umbrella is placed over the head of someone while indoors.
75
It's bad luck to leave a house through a different door than the one used to come into it.
143
At times, a horseshoe may be found above doorways. When positioned like a regular 'U' it supposedly collects luck. However, when it is positioned like an upside-down 'U' the luck supposedly drains.
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Placing keys on a table is considered unlucky. (Sweden)
3
Once a wedding ring has been placed on the finger, it is considered bad luck to remove it.
117
Many believe that if all of the candles on a birthday cake are blown out with one breath, while making a silent wish, the wish will come true.
298
Placing a hat on the bed is, apparently, bad luck. (South Carolina)
9